An international collaborative study is proposed to assess the effects on reproductive outcomes of occupational exposures to aromatic solvents in the oil refinery industry. This study takes advantage of unique characteristics of the urban Chinese health care system which makes feasible the collection of accurate measures of the number of women attempting to conceive and accurate follow-up of the reproductive outcomes. In China, a married couple must obtain permission from the local family planning administration before attempting to conceive. A total of 600 married women (150 for each of four well-defined exposure groups: benzene exposed, toluene exposed, styrene exposed and unexposed) who obtain birth permission from the family planning administration between February 1994 and August 1996, will be registered and invited to participate in the study. Preliminary studies suggest that participation should be greater than 95%. Upon enrollment each woman and her husband will have occupational exposures evaluated by questionnaire. Relevant exposures to specific chemicals will be evaluated based on job title and work sites. The specific chemicals of interest include benzene, toluene, styrene and their derivatives. Environmental exposure assessment will be performed with collection of personal and area samples, and detailed diary information. Benzene, toluene, and styrene concentrations in the air will be measured to estimate the exposure. Information on other covariates or confounders, including smoking, indoor pollution sources, diet, and physical activity at work/home will be evaluated from the questionnaire. After the initial visit, each woman will be requested to provide a daily urine sample and to keep a diary for her menstrual period, symptoms, sexual activity, general health status, medication, cigarette smoking, alcohol consumption, and physical activity. Time to conception as well as sub-clinical miscarriage will be monitored by using the recently developed, highly sensitive and specific biochemical assay for measurement of daily urinary human chorionic gonadotropin (beta-hCG). When a woman develops early signs or symptoms of pregnancy, she will be evaluated at her regular hospital, where she will also receive routine prenatal care, delivery services and postnatal care. Reproductive endpoints will include menstrual disturbances, time to conception, fecundability, spontaneous abortion, preterm labor, preterm delivery, intrauterine growth retardation, malformations and still birth. Associations of adverse reproductive outcomes with occupational and environmental exposures can be efficiently quantified, controlling for personal behavior in this unique population.